Ballscrew arrangements are widely used in a variety of applications where adjustment or other movement of a portion of a manipulator device along a linear axis is desired. Most commonly, a ballscrew nut is threadedly mounted on the ballscrew, and relative rotation between the ballscrew and the ballscrew nut causes translation of either the ballscrew nut relative the ballscrew along its longitudinal axis or the ballscrew relative the ballscrew nut (depending on which part is held stationary) as a result of the threaded interaction between these parts. Direction of displacement of the ballscrew nut (or the ballscrew) along the linear axis depends upon the direction of the relative rotation between the ballscrew and the ballscrew nut.
Connection of the ballscrew nut and its associated structure to the manipulator device is conventionally accomplished by a relatively rigid arrangement. In operation, the reciprocation of an extension element or other movable part of the device along the ballscrew's linear axis often imposes eccentric loads on the ballscrew nut relative the ballscrew as a result of rocking motions or other deflections caused by the mass of the movable part itself, various payloads affected by such movable parts, sudden stops or starts of movement, and the like. As a result of such eccentric loads, the alignment of the ballscrew nut vis-a-vis the ballscrew may be adversely affected, causing the threads of the ballscrew nut to be slightly misaligned vis-a-vis the corresponding threads of the ballscrew. Such misalignment can cause binding interaction between the ballscrew nut and the ballscrew, inconsistent performance or movement of the ballscrew nut along the ballscrew, premature fatigue failure, introduction of backlash or slack into the system, and, possibly, literal destruction of the threaded interacting surfaces of these parts. In robotic applications in particular, such premature wear and failure of various ballscrew parts deceases reliability and safety of the mechanisms, and increases costs to the industry.
Linear slides and rotary trunnion mountings have often been utilized in the industry to provide alignment tolerances to various moving parts, including ballscrew arrangements; however, such systems have proved to he expensive, inconvenient and bulky, and subject to excessive wear (thereby increasing the clearances within the system and allowing backlash and further misalignment to propagate). Moreover, linear slides such as dovetail trunnion mountings, require duplicative structures to provide for multidirectional freedoms of movement. Such inefficiency adds to the complexity and cost, and reduces reliability of such a system.
Consequently, despite the wide-range use of ballscrew devices for various applications, the industry has heretofore failed to provide a ballscrew and ballscrew nut arrangement which simply, automatically, and consistently maintains proper alignment under varying conditions and loads applied to a system. As a result, there remain problems of providing a dependable ballscrew arrangement which can adapt automatically to variations in its ballscrew/ballscrew nut alignment while maintaining overall stiffness or rigidity of the system and minimizing slack or backlash in the system.